1. Field of the Invention
The present invention relates to an oxyfuel combustion boiler plant and an operating method for the oxyfuel combustion boiler plant.
2. Description of Related Art
A thermal power plant including a boiler and a steam turbine as main components is pointed out that the discharge quantity of carbon dioxide that is a global warming factor is larger than those of other power generation systems.
Therefore, when burning fuel by a boiler, a method for burning fuel using high-purity oxygen instead of air is proposed. Hereinafter, a burning method using oxygen is called oxyfuel combustion and a burning method using air is called air combustion.
The oxyfuel combustion changes the greater part of exhaust gas to carbon dioxide. Therefore, when capturing carbon dioxide from exhaust gas, there is no need to concentrate carbon dioxide and the exhaust gas is directly cooled, thus the carbon dioxide can be liquefied and separated. Therefore, oxyfuel combustion is one of the methods effective in deletion of the carbon dioxide discharge quantity.
Further, the oxyfuel combustion, since nitrogen making up about 80% of the air is not supplied to the boiler, does not generate a nitrogen oxide (thermal NOx) generated from nitrogen in the air. Therefore, the reduction effect of nitrogen oxide can be expected.
However, the oxyfuel combustion boiler burns fuel using high-purity oxygen instead of air, so that the flame temperature rises extremely, thus there is a fear that the burner and boiler furnace wall surface may be damaged. Therefore, a system for circulating a part of the exhaust gas of the boiler and mixing and burning the oxygen and exhaust gas of the boiler is proposed.
Patent Document 1 describes a method for burning fuel using the air combustion system as usual at the start time and then shifting to the oxyfuel combustion system.    Patent Document 1: Japanese Patent Laid-open No. 2001-336736